(a) Technical Field
The present invention relates to a camera for detecting a driver's drowsiness. More particularly, it relates to a camera for detecting a driver's state of drowsiness, which can increase the number of pixels in an image of the driver's eyes without using a high definition camera.
(b) Background Art
Japanese Patent Application Publication No. 1998-035320 describes a vehicle condition detector, in which a charge coupled device (CCD) camera, as an image sensor, is mounted in an image pickup part to collect an image of a driver's face. The image of the driver's face is displayed in an enlarged size on a display screen, and an eye area is extracted from the image of the driver's face to determine the state of the driver's drowsiness.
Japanese Patent Application Publication No. 2003-271931 describe an image magnifier, in which an image of a driver's eyes is magnified to determine the driver's drowsiness state. Here, a method for reducing the effect of noise included in an original image (i.e., an image before magnification) is applied to an image after magnification.
In particular, when the image data composed of a plurality of pixels is magnified by the image magnifier, all pixels other than the pixels at an end part in the image data after magnification are generated by interpolation from the plurality of pixel data of the image data before magnification. According to this method, the information of the plurality of pixels before magnification is squeezed into all pixels other than the pixels at the end part in the image after magnification. And, the pixels generated using the pixel data of the image data before magnification, which has noise, are affected by the other pixels, which have no noise. Therefore, the image can be magnified while reducing the effect of the noise present in the image before magnification. However, a considerable amount of time is required to process the image data by software, and, thus, it is not possible to process the image data within a predetermined sampling time.
In the case where the opening and closing of a driver's eyes is detected by a system for detecting a driver's drowsiness state, the pixel data present between the upper and the lower eyelids is as small as 10 pixels in a video graphic array (VGA) camera. As shown in FIG. 4, the resolution of the degree of opening of an eye depends on the number of pixels. Therefore, it may be difficult to determine from the image having a small number of pixels whether the upper and lower eyelids are opened or closed. For example, even when using a high pixel image sensor in which one pixel is increased to four pixels, the brightness of one pixel in the high pixel image sensor is reduced to ¼, and thus the image analysis cannot be simply and easily performed even if the number of pixels increases.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.